A global navigation satellite system (GNSS) receiver receives signals from satellites. This GNSS receiver simultaneously generates replicas of those same signals. Upon receiving the transmitted signal, the GNSS receiver calculates the satellite range measurements based on the time it took the satellite signals to reach the GNSS receiver. These range measurements are, however, pseudorange measurements because the GNSS receiver does not generate the replicas exactly coincidental to the satellite due to the clock offset in the receiver.
In some embodiments, a GNSS receiver can be part of a ground-based augmentation system (GBAS). A GBAS station includes a set of GNSS receivers, also referred to herein as reference receivers (RRs), which help provide correction data to other GNSS receivers. More specifically, a GBAS station can compare the known distance between the satellite and the GNSS receiver and the computed pseudorange distance. Then, based on this difference, a GBAS station can compute correction data for the satellite signals, along with the 1-sigma for the correction data. This information is then broadcast to other GNSS receivers to aid in calculating their own positions. A broadcast of this type is also referred to as a Type 1 Broadcast. As a result, a GBAS station can increase the positional accuracy of GNSS receivers in the GNSS, which is beneficial for many applications, including precision aircraft approaches.
RRs included in a GBAS station can be subject to broadband radio frequency interference (RFI) that can affect the accuracy of the correction data. For example, when a global positioning system (GPS) RR (i.e., a RR incorporated in the satellite system in the United States) is subjected to an interfering broadband signal that exceeds power density levels of −110.5 dBm/MHz within the GPS L1 (1575.42 MHz) band, the GPS RR will experience a drop in signal to noise ratio (C/N0) across all tracked satellites. While GPS is used as an example here, other satellite systems can be similarly affected by an interfering broadband signal, such as Galileo, etc. A satellite measurement calculated with a satellite signal that has a C/N0 value below a minimum operating level will be excluded from use in the formation of differential correction data and from use in some integrity monitoring functions of the GBAS station. In some instances, after a period of time, the power of the interfering broadband signal decreases and/or the C/N0 of the satellite signal increases. The problem then becomes, how quickly and with what certainty should the excluded satellite measurements be reaccepted into differential correction data and integrity monitoring.
For the reasons stated above and for reasons stated below which will become apparent to those skilled in the art upon reading and understanding the specification, there is a need in the art for improved systems and methods for readmittance of excluded satellite measurements in differential correction data and integrity monitors of a GBAS station.